1. Field of the Invention
This invention relates generally to a tool for handling high torque in a nuclear reactor pressure vessel.
2. Description of Related Art
Repairs and inspections performed within a reactor pressure vessel (RPV) such as a boiling water reactor (BWR) are generally performed with ropes and poles for manual manipulation of tools and/or delivery of dedicated automated tools. The RPV is generally a cylindrical shaped vessel and is closed at both ends (e.g., a bottom head and a removable top head). During a reactor shut down, the top head of the RPV is removed so as to inspect or repair a selected component within. Other components in the RPV located between a top guide and a core plate or below the core plate may also be removed. To perform the inspections and/or repairs, an operator stands on a bridge positioned over the RPV and lowers the tool using ropes and poles, which may extend about eighty (80) feet below. The ability to perform such inspections and/or repairs depends on the dexterity of the operator.
Due to the difficulty in accessing certain locations within the RPV, performing the repairs and/or inspections at such locations can be time consuming and burdensome. It is desirable to limit the time required to perform the repairs and/or inspections in a RPV, due to the enormous daily cost of the reactor being shut down (up to almost a million dollars a day in lost revenue). Reducing the amount of time required to perform such inspections and/or repairs also would facilitate reducing radiation exposure to operators, technicians and maintenance personnel, for example.
An approach to repairing and/or inspecting equipments in the RPV has been to use handling poles to attach tools for repairing and servicing. The handling poles are light-weight and thus easy to maneuver within the RPV. Further, handling poles may be designed specifically to handle high-torque. The handling poles may be generally constructed in 10-foot sections and assembled to work in depths of over 80 feet.
However, conventional handling poles typically fail at connection joints at approximately 50 ft lbs of torque. Hence, a way to produce higher torque has been to use heavier poles in excess of 130 lbs to deliver the torque. But heavier poles require the use of a overhead crane to assemble the poles and lift the assembled pole to its location. In addition, it may be desirable to keep the weight of the poles as low as possible in order to allow extended use by an operator. Thus, heavier poles are less desirable than the smaller, lighter handling poles.
Another approach to generate the high-torque for handling poles has been to use a torque multiplier. However, a torque multiplier is generally larger in size than the smaller handling pole and requires additional readings and calibrations.